ci: add GitHub Actions workflow for Windows x64 GUI build

- MSVC + vcpkg + Qt6 + OpenCV + LibRaw
- vcpkg binary caching for faster CI runs
- windeployqt for Qt DLL bundling
- Upload artifact on every push
- Create ZIP and attach to GitHub Release on git tags

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/windows.yml

@@ -0,0 +1,87 @@
+name: Windows Build
+
+on:
+  push:
+    branches: [main]
+    tags:     ['v*']
+  pull_request:
+    branches: [main]
+
+jobs:
+  build-windows:
+    name: Windows x64 (MSVC + vcpkg)
+    runs-on: windows-latest
+
+    env:
+      VCPKG_DEFAULT_TRIPLET: x64-windows
+      # vcpkg Binary Caching → deutlich schnellere CI-Durchläufe
+      VCPKG_BINARY_SOURCES: "clear;x-gha,readwrite"
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      # vcpkg Binary Cache via GitHub Actions Cache
+      - name: Export GitHub Actions cache vars
+        uses: actions/github-script@v7
+        with:
+          script: |
+            core.exportVariable('ACTIONS_CACHE_URL',    process.env.ACTIONS_CACHE_URL    || '');
+            core.exportVariable('ACTIONS_RUNTIME_TOKEN', process.env.ACTIONS_RUNTIME_TOKEN || '');
+
+      - name: Setup vcpkg
+        uses: lukka/run-vcpkg@v11
+        with:
+          vcpkgGitCommitId: '0a66b5fd01fc1515eb7a48c6dc5b1dcc1ce2f6bc'  # stable snapshot
+
+      - name: Install dependencies via vcpkg
+        run: |
+          vcpkg install opencv4:x64-windows libraw:x64-windows qt:x64-windows
+        shell: pwsh
+
+      - name: Configure CMake
+        run: |
+          cmake -B build -G Ninja `
+            -DCMAKE_BUILD_TYPE=Release `
+            -DCMAKE_TOOLCHAIN_FILE="$env:VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake" `
+            -DVCPKG_TARGET_TRIPLET=x64-windows `
+            -DBUILD_GUI=ON `
+            -DBUILD_TESTS=OFF
+        shell: pwsh
+
+      - name: Build
+        run: cmake --build build --config Release --parallel
+        shell: pwsh
+
+      - name: Install (collect EXE + DLLs)
+        run: cmake --install build --prefix dist
+        shell: pwsh
+
+      - name: Deploy Qt DLLs (windeployqt)
+        run: |
+          $qtBin = (Get-ChildItem "$env:VCPKG_ROOT/installed/x64-windows/tools/qt6/bin" -Filter "windeployqt*.exe" -ErrorAction SilentlyContinue | Select-Object -First 1)?.FullName
+          if ($qtBin) {
+            & $qtBin --release --no-translations dist/bin/negative-converter.exe
+          } else {
+            Write-Warning "windeployqt not found, skipping Qt DLL deployment"
+          }
+        shell: pwsh
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: negative-converter-windows-x64
+          path: dist/
+          if-no-files-found: error
+
+      # Nur bei Git-Tags: Release erstellen und ZIP anhängen
+      - name: Create ZIP for release
+        if: startsWith(github.ref, 'refs/tags/')
+        run: Compress-Archive -Path dist/* -DestinationPath negative-converter-windows-x64.zip
+        shell: pwsh
+
+      - name: Upload to GitHub Release
+        if: startsWith(github.ref, 'refs/tags/')
+        uses: softprops/action-gh-release@v2
+        with:
+          files: negative-converter-windows-x64.zip